Prior Art
In the production of petroleum crude from subsurface formations containing highly viscous crude, it has become the practice to inject into the formations a steam or hot fluid for the purpose of increasing the temperature of the formation, thus increasing the mobility of the crude so that it may flow from the formation into a producing well. Apparatus for use in such a production arrangement generally includes a means at the wellhead for generating the steam or hot fluid and a cased well including injection tubing that is used for transporting the steam or hot fluid from the surface to the subsurface location. At the subsurface location a packer is usually provided to prevent the steam or hot fluids from flowing back up the annulus between the injection tubing and the casing thus insuring that the steam is forced into the formation for heating the viscous crude in place.
The packers that had been used with such a subsurface formation completion scheme have functioned adequately when the temperature of the injection fluid and the pressures at the subsurface are reasonably low. However, as temperatures and pressures have increased, to the ranges of 550.degree. to 650.degree. F. and 2000 to 2500 psi, it has been found that the available subsurface packers have not been capable of maintaining an adequate seal in the annulus and the injection fluid sometimes bypasses the packer and fills the annulus within the casing between the injection string and the casing. Such a bypass of the injection fluid has two serious consequences in a steam injection well. Firstly, the steam surrounding the injection string provides a heat conduction path for withdrawing heat from the injection string and in that way reduces the amount of heat that is actually injected into the petroleum containing formation. Secondly, the loss of injection fluids into the annulus reduces the amount of fluids that will be transported back into the formation to accomplish the desired heating of the formation. An improved subsurface packing assembly and injection scheme is therefore desirable in the petroleum industry.